In the DIDON network, the binary data are transmitted in packets using NRZ coded amplitude modulation on picture lines of broadcasted television at the bit rate of 6.2 Mbit/s. The broadcast channel introduces a number of perturbations to the video signal, such as selective fades, noise and echoes resulting from reflections occurring near the location of the receiver. The impulse response is thus distorted. Considering the high bit rate used, a piggyback phenomenon occurs among impulses, that is, an intersymbol interference phenomenon. As the echo phenomena increase the sensitivity of the signal to noise and other parasitics, it is important to provide an echo canceller in the receivers of the DIDON data network.
In the text "TELEINFORMATIQUE Transport et Traitement de L'information dans les Resaux et Systemes Teleinformatiques", by C. Machi and J. F. Guibert (Ed. DUNOD 1979), the intersymbol interference phenomenon is discussed in section 3.1.4. To reduce these interferences, a linear receiver with digital filter, later adaptive, as indicated in section 3.3.3.F is provided. A linear digital filter is described in section A.2.2. of that same text.